Mobile IP technology is a solution for seamless mobility on a network such as, for instance, the global Internet or a private network that is scalable, robust and secure, and that allows roaming or mobile entities (also commonly referred to in the art as mobile nodes) such as radios, phones, laptops, Personal Digital Assistants (PDAs), etc., to maintain ongoing communications while changing their point of attachment to the network. Mobile IP protocols are described in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 3344 titled “IP Mobility Support for IPv4” (also commonly referred to in the art as MIPv4 and wherein IPv4 is described in RFC 791) and in RFC 3775 titled “Mobility Support in IPv6” (also commonly referred to in the art as MIPv6 and wherein IPv6 is described in RFC 2460). Both MIPv4 and MIPv6 are referred to herein as standard Mobile IP.
More specifically, in accordance with standard Mobile IP, each mobile entity is always identified by a home address (HoA) (regardless of its current point of attachment to the network), which provides information about its point of attachment to a home network. However, when the mobile entity is connected to the network outside of its home network, i.e. when visiting a foreign network or a foreign domain, the mobile entity is also associated with a care-of address (CoA) that provides information about its current point of attachment. Moreover, in Mobile IP enabled networks (i.e., networks in which multiple (two or more) entities implement standard Mobile IP), a client-server approach may be used, for example, to facilitate secure communications. For such an approach, a server in a mobile entity's home network may have the functionality, among other functionality, for authenticating the mobile entity prior to the mobile entity being allowed to communicate with other entities within a network. A client-server model may also be used for other purposes as is well known in the art, such as virtual private network (VPN) functions.
IP Multicasting is a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information comprising one or more packets to a plurality of recipients, wherein a packet is defined generally herein as a message transmitted over a network from one entity to another entity and may include, but is not limited to, an IP datagram. IP Multicasting is described in RFC 1112 titled “Host Extensions for IP Multicasting” and is also referred to herein as standard IP Multicasting. In accordance with standard IP Multicasting, an entity may join an IP multicast group (also referred to herein as a “native” multicast group) that is associated with or identified by an assigned IP multicast address. Thereafter, standard IP Multicasting is used to facilitate delivering source traffic (i.e., packets) to multiple receivers (i.e., group members) that have joined the multicast group, thereby, minimizing bandwidth since these packets do not need to be individually unicast to each of the members of the multicast group. This bandwidth savings makes the use of IP Multicasting technology desirable within any network including a Mobile IP enabled network.
Multicast communication, however, is not optimally supported for mobile entities that implement Mobile IP. This is because typically either the multicast nature of a communication is lost (due to unicast encapsulation and delivery of multicast packets), or the client-server model of communication is not preserved (due to receipt by a mobile entity of multicast packets directly without first going through a server such as one described above).
More particularly, standard Mobile IP supports two methods of receiving multicast packets. In the first method, multicast packets are sent to a home agent that joins a multicast group on behalf of a mobile entity, and the home agent then tunnels these packets in unicast to the mobile entity. A home agent is a mobility server in the mobile entity's home network with which the mobile entity registers a care-of-address when the mobile entity is in a foreign network. The home agent registration enables the home agent to send packets destined for the mobile entity through a tunnel to the care-of-address, wherein upon arriving at the end of the tunnel the packets are delivered to the mobile entity. A tunnel is the path followed by a packet while it is encapsulated. The model is that while encapsulated, a packet is routed to a knowledgeable decapsulating agent, which decapsulates the packet and then correctly delivers it to its ultimate destination. In the second method for receiving multicast packets in a Mobile IP enabled network, mobile entities join multicast groups directly and packets reach them natively using standard IP Multicasting.
Accordingly, for the first method the multicast nature of the traffic is lost, which degrades the potential bandwidth savings from using multicast communications. For the second method the client-server model is lost, which may adversely impact secure communications in the network. This loss of secure communications may be undesirable in networks where secure communications are critical, such as in Public Safety applications.
Thus, there exists a need for a method and apparatus for multicast communications within Mobile IP enabled networks that both preserves the client-server model and realizes more of the potential bandwidth savings of using IP Multicasting.